RCP8.5 tracks cumulative CO2 emissions

Abstract

Climate simulation-based scenarios are routinely used to characterize a range of plausible climate futures. Despite some recent progress on bending the emissions curve, RCP8.5, the most aggressive scenario in assumed fossil fuel use for global climate models, will continue to serve as a useful tool for quantifying physical climate risk, especially over near- to midterm policy-relevant time horizons. Not only are the emissions consistent with RCP8.5 in close agreement with historical total cumulative CO₂ emissions (within 1%), but RCP8.5 is also the best match out to midcentury under current and stated policies with still highly plausible levels of CO₂ emissions in 2100.

Keywords: CO2 emissions; business as usual; climate change.

Fig. 1.

Total cumulative CO₂ emissions since 2005 through 2020, 2030, and 2050. Data sources: Historical data from Global Carbon Project (6); emissions consistent with RCPs are from RCP Database Version 2.0.5 (https://tntcat.iiasa.ac.at/RcpDb/); “business as usual” and “business as intended” are from IEA Current Policies and Stated Policies scenarios, respectively (9). IEA data (fossil fuel from energy use only) was combined with future land use and industrial emissions to estimate total CO₂ emissions. Future land use emissions estimated from linear trend fit to 2005 to 2019 Global Carbon Project land use emissions data (6). Industrial emissions estimated as 10% of total emissions. Final IEA data use historical values through 2020 and scenario values thereafter. Biotic feedbacks are not included in any IEA-based estimate. Note that RCP forcing levels are intended to represent the sum of biotic feedbacks and human emissions.